The principle of operation and chosen examples of construction of SI engines designed to be powered with aviation fuel (Heavy Fuel Engines – HFE) have been presented in the article. Contemporary solutions of the HFE combustion system constitute the further development of a patent of an Australian company Orbital working in the field of two-stroke SI engines. Engines of this type, characterized by low weight and low value of specific fuel consumption, are used among others for the propulsion of drones (Unmanned Aerial Vehicles – UAV), where range and endurance are essential parameters. That is also a practical realization of the military logistical concept of using a "single fuel in the battlefield".